Catalyst control for six-cycle engine

ABSTRACT

A six-cycle engine has the advantage for the capability of internal cooling with scavenging air. This advantage enables the compressive ratio to rise, thereby achieving lower fuel consumption. However, there has been a critical problem due to lowered temperature of the exhaust catalyst and excessive volume of oxygen contained therein caused by the mixing of the scavenging air with exhaust gas. To solve the problem of lowered temperature, the invention has thermally insulated the fuel combustion chamber and the exhausting system, and controlled the aperture degree of the scavenging port valve relatively to the suction valve to adjust the scavenging air volume against the suction air, thereby controlling temperature of the exhaust gas. Further, to solve the problem of excessive volume of oxygen, the invention has introduced an EGR (Exhaust Gas Recirculation) system to fully substitute the scavenging air with circulating exhaust gas and a self EGR system to open the exhaust valve during the scavenging air introduction stroke. The present invention has successfully made a naturally good fuel-efficient six-cycle internal combustion engine be suited one for practical use such as conventional vehicles.

The present invention relates to a method and a system for controllingactual condition of an exhaust catalyst installed in a six-cycle engine.

There is a known premix combustion type six-cycle engine consisting of afuel feeding device, an suction port that feeds air-fuel mixture, and ascavenging port that solely feeds fresh air thereto (Refer to theReference Japanese Patent Publication 1 for example). Further, there isa known method for operating a six-cycle engine that does not have thescavenging air feeding port, but opens an exhaust valve and introduceexhaust gas therein at scavenging introduction stroke. There is a knownfact proving that the this method was practically applied to fuel savingcompetition vehicles and enabled them to score satisfactory results ascited in a non-patent technical literature 1 listed below for example.There are a variety of known types in the variable valve timingmechanism that is operated via switching of a cam that drives the valvein response to the operating condition of an engine as cited in theReference Japanese Patent Publication 2 for example.

The continuously variable valve timing mechanism serves as a substitutefor a throttle valve. It is well known that this mechanism makes pumpingloss be lowered as cited in the Reference Japanese Patent Publication 2for example.

Reference Japanese Patent Publications:

1: Laid-Open Japanese Utility Model HEISEI-2-96435 (1990) 2: Laid-OpenJapanese Patent HEISEI-5-179913 (1993) 3: Laid-Open Japanese PatentSHOWA-55-137305 (1980)

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Non-Patent Technical Literature 1:

Automobile Technology, 2004, Vol. 58, No. 10, page 27

Any of conventional six-cycle engines features its capability to lowertemperature of the fuel combustion chamber due to presence of scavengingair introduction stroke and scavenging air exhaust stroke so as torealize a higher compression ratio than that is obtainable by any offour-cycle engines, thereby resulting in the improved fuel combustion.In order to stably operate an A/F sensor to detect oxygen density in theexhaust gas, the six-cycle engine cited in the above patent publication1 was provided with a couple of exhaust ports: one was for exhaustingcombusted gas and another for exhausting scavenging gas. However,practically, reaction rate of the catalyst sensor was not quite fast,causing only a mean value of the oxygen density detected, thereforethere was not any critical problem. Conversely, combusted gas remainingin the fuel combustion chamber mixes with the scavenging air, causing aproblem of which the combusted gas is discharged without post treatment.Hence, as in the conventional six-cycle engine cited in the above patentpublication 1, the present invention takes measures to discharge thewhole of exhaust gas and the scavenging exhaust gas via a catalyst. Thepresent invention further controls valve aperture degree of thescavenging port to solve the problems of increased temperature andexcess of oxygen in the catalyst both of which caused by the abovemeasures.

When only one exhaust port is provided, it will cause the exhaust gas tomix with the scavenging air, causing lowering temperature of an exhaustcatalyst thus leading to the difficulty in activation of the catalyst.This problem can be solved by preserving temperature of the exhaust gasemitted from the six-cycle engine. Concretely, not only for the fuelcombustion chamber, but also inner wall of the exhaust port includingthe catalyst is insulated with heat insulating material in order tomaintain temperature of the exhaust gas. In this case, since temperatureof the exhaust catalyst tends to excessively rise, sufficient careshould be taken to secure a cooling means for properly adjusting thetemperature thereof. The present invention provides a proper coolingmeans for adjusting temperature of the exhaust catalyst.

Likewise, when scavenging air is composed of fresh air, catalyticmaterial bears excessive oxygen. This may cause inactivation ofreductive action of the catalyst. To cope with this problem, in case offour-cycle engines, measures has been taken such as increasing amount offuel injection and providing an “Exhaust Gas Recirculation” (EGR) systemto circulate exhaust gas to intake air. Conversely, in the case of thesix-cycle engine, scavenging air remains even after fuel combustion,leading to the problem of excess of oxygen persisting even ifintroducing the above systems Further, other problems arise such aspresence of the scavenging air obliges the dimension of the above EGRsystem to be enlarged and the process for warming up this systeminevitably consumes a longer time.

The term “Direct Injection Type Engine” specifically cited in thepresent invention collectively refers to the compression ignitionengines such as diesel engines and the spark ignition engines thatdirectly inject fuel such as gasoline into cylinders. Further,generally, the first and second valves include the butterfly valves orthe slide valves used as throttle valves that are set to suction andscavenging ports. However, in the present invention, suction andscavenging poppet valves are also included, where the suction andscavenging poppet valves respectively operate with a continuouslyvariable valve timing mechanism that continuously controls the openangle and the lifting height of the above valves against the rotationsof the engine cranks. By providing the first and second valves with thecontinuously variable valve timing mechanism, when restricting the gasinflow rate in the suction and scavenging stroke, the above mechanismeliminates the pressure decline inside the first and second valves,thereby reducing the pumping loss. Hence, any of the six-cycle enginesincorporating the above mechanism enhances the fuel combustionefficiency.

The first means for solving problems consists of a premix combustiontype six-cycle engine comprising: a first valve and a fuel supplyingdevice disposed in a suction port; and a second valve disposed in ascavenging port, each of the first and second valves including means foroperating in linkages with an accelerating operation and another meansfor relatively varying the aperture degrees of the first and secondvalves via operation of an actuator.

The second means for solving problems consists of a direct injectiontype six-cycle engine comprising: a first valve disposed in a suctionport; a second valve disposed in a scavenging port, each of the firstand second valves including means for operating in linkages with anaccelerating operation and another means for relatively varying theaperture degrees of the first and second valves via operation of anactuator; and a system for totally substituting scavenging air withcirculating exhaust gas.

The third means for solving problems consists of the six-cycle engineaccording to the first means for solving problems, comprising a systemfor totally substituting scavenging air with circulating exhaust gas.

The fourth means for solving problems consists of the six-cycle engineaccording to the first means for solving problems, comprising a suctionvalve and a scavenging valve both opened in a suction stroke.

The fifth means for solving problems consists of the six-cycle engineaccording to claim 2, comprising a mechanism for opening a suction valvein a scavenging air introducing stroke, said mechanism furthercontinuously varying the open angle of said suction valve in thescavenging air introducing stroke.

The sixth means for solving problems consists of a valve controllingsystem for the six-cycle engine according to the first to fifth meansfor solving problems comprising means for sensing actual temperature ofan exhaust catalyst itself and means for driving an actuator thatrelatively controls the aperture degrees of the first valve and thesecond valve in accordance with the actual temperature of the exhaustcatalyst.

The seventh means for solving problems consists of the six-cycle engineaccording to claims 1 to 5, comprising a variable valve timing mechanismdisposed in an exhaust valve, said variable valve timing mechanismincluding: the normal mode to open the exhaust valve during an exhauststroke and a scavenging air introducing stroke; and the warm-up mode toopen the exhaust valve during the exhaust stroke, the scavenging airintroducing stroke and a scavenging air exhausting stroke, said modesbeing capable of shifting itself between the normal mode and the warm-upmode.

The eighth means for solving problems consists of a valve controllingsystem having a computer for the variable valve timing mechanism builtin the six-cycle engine according to the seventh means for solvingproblems, said computer comprising means for sensing actual condition ofthe exhaust catalyst and means for driving an actuator to vary the openangle of the exhaust valve of the variable valve timing mechanism.

The ninth means for solving problems consist of the six-cycle engineaccording to the first to fifth means for solving problems, comprising:a scavenging port valve that is disposed on the upper stream side of thescavenging port independently of the second valve; and an independentport that is disposed between the scavenging port valve and the secondvalve so as to enable an exhaust port to circularly supply exhaust gasthereto.

The tenth means for solving problems consists of a valve controllingsystem having a computer for the scavenging port valve of the six-cycleengine according to the ninth means for solving problems, said computercomprising means for sensing the actual condition of the exhaustcatalyst, means for sensing aperture degree of the first valve, andmeans for driving an actuator to vary the aperture degree of thescavenging port valve.

The first means for solving problems according to the present inventionhas an advantage of properly controlling temperature of exhaust gasemitted from a premix combustion type six-cycle engine. For example,when temperature of an exhaust catalyst remains low, aperture degree ofthe second valve is narrowed relatively to the aperture degree of thefirst valve for a normal load so as to decrease the scavenging air rate.Whenever necessary, the second valve is closed. In this way, it ispossible to decrease the scavenging air rate, raise the temperature ofexhaust gas and the exhaust catalyst. This action is also effective forcontracting the time required for warming up the engine and raising thecatalyst temperature faster. Conversely, if the temperature of theexhaust catalyst remains high, relatively increasing the aperture degreeof the second valve can raise the proportion of the scavenging air andlower the temperature of the exhaust gas and the catalyst. Concurrently,resistance in the exhaust path is decreased in the scavenging airintroducing stroke, thereby decreasing the pumping loss. This is becausethe aperture degree of the second valve can be controlled independentlyof the first valve although the second valve operates in association ofthe first valve that serves as the throttle valve for control of exhausttemperature. This can be done because, unlike the first valve thataffects the amount of intake air, the opening and closing operations ofthe second valve hardly affect the engine output power.

The second means for solving problems according to the present inventionprovides a further advantage by way of solving problems that cause theexhaust catalyst built in the direct injection type six-cycle engine tobear excessive volume of oxygen so as to properly control temperature ofthe exhaust gas. The second means properly controls temperature of thecatalyst via the same method as adopted for the first means for solvingproblems. Generally, circulating exhaust gas is subject to a coolingprocess before being used as scavenging air. Compared to the process foruniformly mixing circulative gas without discriminating between suctionair and scavenging air, oxygen density of suction air remainsinvariable, thereby amount of fuel supply being not required todecrease. In this way, it becomes possible to properly controltemperature of catalyst without lowering the output power. Unlike theExhaust Gas Recirculation for a four-cycle engine, the second means forsolving problems basically substitutes the whole scavenging air with thecirculating exhaust gas. Although the volume of circulating gasincreases, the structure is thus quite simple. More accurate control ofoxygen density is done by properly adjusting the fuel injection volumeagainst the volume of fresh air contained in the suction and scavengingair. When deemed necessary, in the same way as the conventionalfour-cycle engine, circulation gas is also supplied to the suction air.

In the same way as the second means for solving problems, the thirdmeans for solving problems according to the present invention providesan advantage in decreasing excess of oxygen in the exhaust catalystwithout lowering the output power by properly substituting scavengingair inside a premix combustion type six-cycle engine with circulatingexhaust gas.

The fourth means for solving problems according to the present inventionalso provides an advantage of enhancing the maximum output power of thesix-cycle engine. In the course of introducing scavenging air, only thescavenging valve is opened to introduce scavenging air filled with freshair into the cylinders. In the course of suction of air, air-fuelmixture from the suction port and scavenging air from the scavengingport are simultaneously introduced into cylinders and mixed with eachother therein. In the course of suction process, independently of thesuction gas volume from the suction port, densely concentrated air-fuelmixture containing fuel proportional to the sum comprising suction airand scavenging air are introduced to the cylinders so as to generateappropriate air-fuel mixture inside cylinders. This mechanism makes itpossible to contract area of the suction valve and relatively expandarea of the scavenging valve. For this reason, the premix combustiontype engine embodied by the fourth means for solving problems makes itpossible to expand the area of the valve aperture during theintroduction of scavenging air stroke to be equal to that of the suctionvalve of four-cycle engine with two valves. Further, during the suctionstroke that most affects the output power, gas is introduced via thesuction valve and the scavenging valve, thereby making it possible toprovide the overall valve aperture area in excess of that of afour-cycle engine with two valves. These measures make it possible torealize actual rotational number beyond that is achievable by any of thefour-cycle engines. Larger area of the valves also makes it possible toeffectively lower the resistance of gas passages of valves and minimizepumping loss as well.

The fifth means for solving problems according to the present inventionis the “self EGR system” comprising a simple structure capable ofsimultaneously executing control over the temperature of the exhaustcatalyst and the oxygen density of the direct injection type six-cycleengine. Further, the fifth means is also advantageous due to compactconfiguration of the external EGR system and the scavenging means. Sinceany of conventional engines mounted on automobiles is rarely driven atthe maximum output power, it is not practical to provide automobileswith the EGR system having own capacity enough for the maximum outputpower. When the engine is driven at a low rotational number, scavengingair mainly composed of circulative exhaust gas is introduced mainly viathe scavenging port. However, while the engine is driven with a higherrotational number, fresh air enough to suffice the shortage is furtherintroduced via the suction valve. This method makes it possible tocompactly build the scavenging port and valve to enable the dimensionsof the air-suction valve and exhaust valve to be expanded relatively,thereby increasing the engine output power and minimizing pumping loss.Further, the smaller setting volume of circulating exhaust gas makes itpossible to compactly configure the external EGR system, especially thecooling system thereof. When a higher engine output is provisionallyrequired, fresh-air with lower temperature is introduced via theair-suction valve to cool off the combustion chamber. In this case,since the engine is driven with a high output power, there is no fear ofcausing temperature of the exhaust catalyst to be lowered excessively.Although the oxygen density may provisionally become too high, conditionof catalyst can be adjusted by increasing air-fuel mixture ratio whenengine output lowers next time.

The sixth means for solving problems according to the present inventionadvantageously provides a system that automatically and properly adjustsactual temperature of catalyst by initially sensing actual temperatureof the exhaust catalyst, followed by actuating the actuator to vary theaperture degrees of the first and second valves relatively.

The seventh means for solving problems according to the presentinvention advantageously realizes an internal EGR system with a simpleconfiguration, which directly introduces a large volume of exhaust gasfrom the exhaust port in the introduction of scavenging air stroke intothe fuel combustion chamber and then varies the volume thereof. Further,by combining the internal EGR system with the controlling system, theseventh means provides further advantages of automatically controllingactual temperature of the catalyst and the actual density of oxygencontained therein as well as warming of the engine being accelerated.When a premix combustion type four-cycle engine admits fresh air,circulating a large volume of exhaust gas via the exhaust port withoutcooling off it will cause the exhaust gas bearing an extremely hightemperature to contact with air-fuel mixture, leading to failures suchas backfire phenomenon. However, in the case of the six-cycle engine,only the scavenging air devoid of fuel comes into direct contact withthe exhaust gas, thereby enabling to generate the above advantageousfunction.

A six-cycle engine admits fresh air and scavenging air consisting ofcooled circulating exhaust gas into the fuel combustion chamber via thescavenging port during the introduction of scavenging air stroke,thereby cooling off the interior of the fuel combustion chamber.However, compressive ratio has previously been set in anticipation ofthe critical case of the driving condition to enable the enginemechanism to be normally operable all the time, thus, not only duringthe cooled-off condition, but also even after being warmed to someextent, there may be such a case in which there is a less need to cooloff the engine with a scavenging air, which depends on the actualtemperature, actual load, and the loaded duration. The above seventhmeans for solving problems has been invented upon considering that it isnot always necessary to fully cool off the circulating exhaust gas.

The eighth means for solving problems provides a further advantage byway of securing a system that is capable of maintaining proper conditionof the exhaust catalyst via a process for sensing several conditionssuch as temperature of the exhaust catalyst and the density of oxygen toautomatically control the volume of the circulating exhaust gas emittedfrom the exhaust port during the introduction of scavenging air stroke.

The ninth means for solving problems according to the present inventionprovides an advantage of varying the volume of fresh air and the volumeof circulating gas from an external EGR relatively to scavenging air byproperly controlling the aperture degree of the second valve and thescavenging port valve via a simple system. The ninth means has a furtheradvantage because temperature of the catalyst and density of oxygen canbe adjusted by way of combining the above means with an automaticallycontrolling system. In particular, when being combined with the fifthmeans for solving problems, the ninth means for solving problems makesit possible to vary the ratio between the volume of circulating exhaustgas emitted from the exhaust valve via the EGR (Exhaust GasRecirculation) process and the volume of the scavenging air, therebyadvantageously accelerating the warming-up of the engine and preciselycontrolling actual temperature of the exhaust gas.

The tenth means for solving problems according to the present inventionprovides a further advantage of properly maintaining temperature ofcatalyst and density of oxygen. This can be done by sensing actualconditions of temperature of the exhaust catalyst and the density ofoxygen contained therein to automatically control the aperture degreesof the second valve and scavenging port valve and adjust the ratio ofthe circulating volume of exhaust gas contained in the scavenging airvia the external EGR process to fresh air.

FIG. 1 is a plan view of a portion of a cylinder head built in a multicylinder premix combustion type six-cycle engine according to the firstmeans for solving problems as viewed from the piston side, which will bedescribed in the first embodiment for implementing the presentinvention;

FIG. 2 is a lateral view of the same as above (the above-referredcylinder head according to the first embodiment for implementing thepresent invention);

FIG. 3 is a chart illustrating the continuously variable valve timingdriving system serving as the first and second valves according to thesecond embodiment for implementing the present invention;

FIG. 4 is a chart illustrating the EGR (Exhaust Gas Recirculation)system built in the direct injection type six-cycle engine according tothe second means for solving problems based on the third embodiment forimplementing the present invention;

FIG. 5 is a plan view of a cylinder head built in a six-cycle engineused in the first embodiment as viewed from the piston side according tothe fourth means for solving problems, which will be described in thefourth embodiment for implementing the present invention;

FIG. 6 is a plan view of a cylinder head built in a six-cycle engineused in the second embodiment as viewed from the piston side accordingto the fourth means for solving problems, which will be described in thefifth embodiment for implementing the present invention;

FIG. 7 is a chart illustrating the EGR (Exhaust Gas Recirculation)system built in the six-cycle engine according to the fifth means forsolving problems, which will be described in the sixth embodiment forimplementing the present invention;

FIG. 8 is a chart illustrating the continuously variable valve timingdriving system built in the suction valve of the six-cycle engine, whichwill be described in as the sixth embodiment for implementing thepresent invention;

FIG. 9 is a cross-sectional view of a cam shaft for driving the exhaustvalve used in the first embodiment according to the seventh means forsolving problems, which will be described in the seventh embodiment forimplementing the present invention;

FIG. 10 is a graphic chart illustrating the pre-set acceleratingvelocity and the valve-lifting height against the rotational angle ofcrank of the cam shown in FIG. 9;

FIG. 11 is a chart illustrating the exhaust valve driving systemaccording to the second embodiment according to the seventh means forsolving problems, which will be described in the eighth embodiment forimplementing the present invention;

FIG. 12 is a chart illustrating the valve controlling system thatapplies the sixth, eighth, and the tenth means for solving problems,which will be described in the ninth embodiment for implementing thepresent invention;

FIG. 13 is a flowchart for controlling operation of the actuator 93according to the sixth means for solving problems, which will bedescribed in the ninth embodiment for implementing the presentinvention;

FIG. 14 is a map illustrating aperture degree of the second valverelative to aperture degree of the first valve according to the sixthmeans for solving problems, which will be described in the ninthembodiment for implementing the present invention;

FIG. 15 is a map illustrating the method of controlling the exhaustvalve according to the eighth means for solving problems, which will bedescribed in the ninth embodiment for implementing the presentinvention; and

FIG. 16 is a map illustrating the method of controlling the scavengingport valve according to the tenth means for solving problems, which willbe described in the ninth embodiment for implementing the presentinvention.

REFERENCE NUMERALS

-   1: Six-cycle engine-   16: Fuel feeding device-   17: Ignition plug-   18: Direct injection type injector-   20: Cylinder head-   20A, 20B, 20C: Receptors for inserting poppet valve formed in the    cylinder head unit-   21: Suction port-   22: Suction valve-   23: The first valve-   24: A sensor for sensing aperture degree of the first valve-   31: Exhaust port-   32. Exhaust valve-   41: Scavenging port-   42: Scavenging valve-   43: The second valve-   43B: Scavenging port valve-   52: Rotational number sensor-   63: Exhaust catalyst-   68: Catalyst sensor-   81/82: Lever-   83/84: Rod-   85: Link-   91/91B: Actuator-   92: Actuator rod-   93: Exhaust valve actuator-   94: Scavenging port valve actuator-   111: Circulation port-   112: Circulating gas cooling unit-   120: Suction valve timing cam shaft-   121/121B: Suction cam-   123, 123B, 133, 143: Controlling shaft-   124, 124B, 144: Rod-   126, 126B, 136, 146: Rocker arm-   126CF, 136CF, 146CF: Cam follower-   127, 137, 147: Valve lifter-   127RA: Rush adjuster-   127SH, 137SH: Valve lifter shaft-   128, 128B, 148: Locker arm shaft-   129, 129B, 149: Locker arm holder-   130: Exhaust valve timing cam shaft-   131: Normal cam-   131B: Exhaust cam-   132: Warm up cam-   132B: Scavenging cam for the exhaust valve-   138: Eccentric wheel-   139: Spring pin-   141: Scavenging normal cam-   510: Accelerating pedal-   610: Controlling computer

The present invention provides a single exhaust port for the six-cycleengine, wherein the exhaust gas and scavenging exhaust gas are totallysubject to passage through the exhaust catalyst. Further, in order todeal with a problem of lowering temperature of the exhaust catalyst, thetemperature is controlled via thermal insulation of combustion chamberand exhaust system and adjustment of the relative aperture degree of thevalve of the scavenging port against the valve of the suction port. Todeal with a problem of causing the exhaust catalyst to be saturated withan excessive volume of oxygen, the invention has solved the problem byusing the EGR system that fully substitutes the scavenging air withcirculating exhaust gas. Further, to deal with a problem of causing theEGR system to be enlarged itself and another problem of requiring muchtime for warm up, a self EGR system has been provided to enable theexhaust valve to open itself in the introducing of scavenging airstroke.

FIRST EMBODIMENT

The multi cylinder premix combustion type six-cycle engine shown in FIG.1 is provided with three kinds of valve in the fuel combustion chamber,including a suction valve 22, an exhaust valve 32, and a scavengingvalve 42. An ignition plug 17 is disposed at a position apart from thecenter so that the above valves can respectively share a wider area. Asuction port 21 and a scavenging port 41 are independently disposed. Afuel feeding device 16 is linked with the suction port 21 so as to feedair-fuel mixture to the fuel combustion chamber, whereas freshscavenging air is led from the scavenging port 41. The first valve 23functioning as the butterfly valve is secured to the suction port 21,whereas the second valve 43 having the configuration identical to thatof the first valve 23 is secured to the scavenging port 41, where thefirst valve 23 and the second valve 43 are respectively secured to anindependently rotating shaft.

FIG. 2 is a lateral view of a cylinder head 20 as viewed from the upperside of FIG. 1. FIG. 2 illustrates operations performed in the peripheryof the link of the first and second valve controlling systems.Generally, as shown in FIG. 12, in a movable body such as an automobile,by stamping the accelerator pedal or turning the throttle grip that islinked with the throttle valve disposed in the suction port of theengine, the built-in engine is actuated in the direction of opening thethrottle valve. In the first practical embodiment of the presentinvention, the six-cycle engine is also provided with a similar linkagemechanism (not shown) to actuate the first valve 23 corresponding to thethrottle valve in response to the actuating operation performed by adriver. Further, the second valve 43 is linked with the first valve viaa lever 81, a rod 83, a link 85, another rod 84, and another lever 82.An actuator 91 is driven to externally vary the protruding amount ofanother rod 92 in response to actual temperature of exhaust gas. Whilethe exhaust catalyst bears an appropriate temperature, the actuator 91remains in a condition shown in FIG. (A), and then, the second valve 43opens itself to the same aperture degree as the first valve 23. When thedetected value of temperature of the exhaust gas rises (or when it isanticipated that temperature of the exhaust catalyst will rise), asshown in FIG. (B), the actuator 91 is actuated to push a rod 92 thatsupports the fulcrum of a link 85. In response to this action, the rod84 moves in the direction of opening the second valve 43 from theposition of the two-dot chained line so as to feed more scavenging air.Conversely, when the detected value of temperature of the exhaust gas islowered (or when it is anticipated that temperature of the exhaustcatalyst will lower), the rod 92 of the actuator 91 retracts itself tocause the second valve 43 to be closed relatively to the first valve 23,thereby causing the second valve 43 to be operated so as to introduceless scavenging air therein.

The first means for solving problem according to the present inventionis not limited to such a case where the valve linked with theaccelerator pedal and the throttle grip is the first valve 23. It isapparent to those skilled in the art that similar effect can be achievedeven when a throttle valve is disposed against the whole suction portand scavenging port, and in addition, even when disposing another valvethat can be opened and closed by an actuator on the part of adown-stream side suction port or scavenging port. Further, it is alsoallowable to provide an actuator that can directly operate the secondvalve in place of the linkage mechanism in order to operate the actuatorin conjunction with the movement of the first valve via an electroniccontrolling means. The above arrangement is also included in theinventive conception of the first means for solving problems.

SECOND EMBODIMENT

FIG. 3 illustrates the inventive valve driving system provided for thesix-cycle engine based on the first means for solving problems, wherethe valve driving system uses a continuously variable valve timingsystem for the suction valve (as the first valve) and the air scavengingvalve (as the second valve). The cylinder head has been omitted fromFIG. 3. The suction valve 22 and the scavenging valve 42 are configuredwith dimensions being equal to each other. The scavenging valve is shownin the nearer side from viewers. In FIG. 3, component parts (126 to 129)of the suction variable valve timing mechanism including the scavengingvalve are shown in the state overlapped with the component parts forscavenging. When adopting the continuously variable valve timing systeminto the scavenging valve and the suction valve, pressure at the valveportion can be prevented from lowering, making it possible to dispensewith pumping loss, thus, fuel combustion efficiency can be increased forthe partial load conditions in which volume of inflow of intake air andscavenging air must be limited. Not only for the premix combustion typeengines, but the effect for minimizing pumping loss is also achievablewith the direct fuel injection engines. Further, since operators arefree from using care with the pumping loss, there is no need to applythe lean burn in which combustion speed is low. Therefore it is quiteeffective for economizing the combustion cost by faster combustion.

The continuously variable valve timing mechanism applied to the suctionvalve 22 and the air scavenging valve 42 are individually provided witha couple of crank-shaped controlling shafts 123 and 143, which arefurther provided with a link mechanism 85 etc. shown in FIG. 3 with atwo-dot chained line as shown in the first practical embodiment. Thecontinuously variable valve timing mechanism is capable of relativelycontrolling aperture degrees of valves by operating the actuator 91. Inthis embodiment, the above-cited controlling shaft and the cam shaft aredisposed on the upper surface of the cylinder head shown with thetwo-dot chained line. When the exhaust catalyst bears an appropriatetemperature, the actuator 91 enters into the state shown in FIG. 3. Thesuction valve 22 and the scavenging valve 42 are respectively operatedby the link mechanism being linked with both valves so as to provideproportional valve aperture degree. The actuator 91 is driven so as toexternally vary the protruding amount of the rod 92, and then properlyadjusts the aperture degree of the scavenging valve relatively to theaperture degree of the suction valve.

In the above continuously variable valve timing mechanism, cams 121 and141 are respectively provided for the corresponding valve mechanism fora common cam shaft 120. Further, locker arms 126 and 146 provided withcam followers 126CF and 146CF are respectively installed for the cams121 and 141. By operating valve lifters 127 and 147 that individuallyswing in linkage with the swinging movement of the above locker arms 126and 146, each valve is pushed and opened. Each of the continuouslyvariable valve timing mechanism employs rotation of each control shaftto move the locker arms 126 and 146 with locker arm holders 129 and 149along the arc-shaped guide formed by the cylinder heads shown by thetwo-dot chained line through the rods 124 and 144 in the rotatingdirection of the cams. This movement makes it possible to change thepositions of the cam followers relative to the rotating angle of thecams, the opening/closing timing of the above valves, and the point ofaction relative to the valve lifters, thereby changing the amounts ofvalve lift.

The cam shaft according to the practical embodiment of the presentinvention is rotated in the counterclockwise direction. By stamping theaccelerator pedal, the shaft 123 for controlling the suction valvecorresponding to the first valve of the mounted internal combustionengine is rotated in the counterclockwise direction, forcing the shaft123 to be rotated in the direction of expanding the aperture of thevalve. FIG. 3 illustrates an actual condition in which the acceleratorpedal has been stamped to the maximum position where the valve liftingheight has become maximum. When the operator eases up on the acceleratorpedal, the controlling shaft 123 and 143 are rotated in the clockwisedirection against the drawing. As a result, the locker arms 126 and 146respectively shift to the right. This in turn causes the locker arms 128and 148 being the swinging center of the locker arms 126 and 146 torespectively approach the point of action for the valve lifters to causethe valve-lifting height to decrease. Concurrently, the valveopening/closing timing is advanced. The head portion of each poppetvalve has the receptors 20A and 20B formed in the cylinder head. Whenthe valve heads remain in the receptors, the aperture area remains 0 tocause the aperture area of the valve to be opened quickly.

The continuously variable valve timing mechanism according to the secondpractical embodiment is capable of simultaneously varying the open angleand the timing solely via rotations of the controlling shafts 123 and123B. Since the force applied to the locker arms is opposite to eachother, the applied forces substantially cancel the opposite force tominimize the supporting torque. Hence, it is possible to operate thecontinuously variable timing mechanism in conjunction with the operatingsystem in the same way as the throttle valve. Even when operating thecontinuously variable timing mechanism with the actuator via theelectronic controlling system, this can be executed by applying lessdriving force.

THIRD EMBODIMENT

FIG. 4 is a conceptual diagram of the EGR system built in the directinjection type three-valve six-cycle engine according to the secondmeans for solving problem. The cylinder heads 20 are illustrated as seenfrom the piston side. The EGR system according to the present embodimenthas an exhaust gas circulating port 111 for circulating exhaust gas froman exhaust port 31 to a scavenging port 41. The exhaust gas circulatingport is equipped with a cooling unit 112 that cools off the exhaust gas.In the introduction of scavenging air stroke, cooled circulating exhaustgas is introduced from the scavenging valve 42. In the suction stroke,fresh air is introduced from the suction valve 22. In the presentembodiment, the first valve 23 and the second valve 43 respectively actthemselves in the same way as in the first embodiment. When a highdegree of temperature has been detected from the exhaust gas, the secondvalve 43 opens itself relatively to the first valve 23. Conversely, whena low degree of temperature has been detected from the exhaust gas, thesecond valve 43 closes itself relatively to the first valve 23.

The six-cycle engine according to the third means for solving problem isthe premix combustion type engine comprising a fuel feeding devicedisposed in the suction port according to the first means for solvingproblems.

FOURTH EMBODIMENT

FIG. 5 is a plan view of the cylinder heads 20 provided for the premixtype six-cycle engine according to the fourth means for solving problemsas viewed from the piston side. In the present embodiment, thescavenging valve 42 and the exhaust valve 32 are configured with largedimensions, whereas the suction valve 22 is configured with relativelysmall dimensions. Air-fuel mixture is supplied from the suction port 21,whereas fresh air is supplied from the scavenging port 41 in the mostcases. In the introduction of scavenging air stroke, only the scavengingvalve 42 opens itself. In the suction stroke, the suction valve 22 opensitself simultaneously with the scavenging valve 42 so as to introduceair-fuel mixture and fresh air therein. A certain volume of fuelrequired for generating single round of explosion is injected into thesuction port 21 with an air-fuel mixture with a density thicker thanthat is fed into any of normal engines. It is so arranged that themixture is further mixed with the scavenging air fed from the scavengingvalve 42 during the suction stroke and the compression stroke so as tofill the cylindrical interior with a predetermined premix condition. Thefourth means for solving problems makes it possible to provide the areaof the scavenging valve 42 to be wider than in the case of disposing thevalves in the six-cycle engine according to the first embodiment. Inparticular, since the valve area in the course of suction that mostaffects the power output becomes the sum of the valve areas of thesuction valve 22 and the scavenging valve 42, the valve area during thesuction stroke exceeds that of the four-cycle engines, thus making itpossible to realize the rotational number being equal to or beyond thatis achievable by any of four-cycle engines. Although not beingillustrated, the first valve and the second valve are also present inthe fourth embodiment, thereby making it possible to properly adjust theair scavenging volume relative to the suction air.

PRACTICAL EMBODIMENT 5

FIG. 6 is a plan view of the five-valve cylinder head 20 according tothe fourth means for solving problems as seen from the piston side. Inthe fourth embodiment, actual sizes of valves are substantially equal toeach other. Total area of individual valves differs via the number ofvalves including two units of the scavenging valve 42, single unit ofthe suction valve, and two units of exhaust valves. Since individualvalves are compactly configured, valves can be opened to full extent viaa minimum lifting height, thereby enabling to raise the number of therotation of the six-cycle engine.

SIXTH EMBODIMENT

FIG. 7 is a plan view of the cylinder head 20 built in the six-cycleengine according to the fifth means for solving problem as viewed fromthe piston side and also an overall schematic view including thecylinder head 20. The scavenging valve 42 built in the six-cycle engineis configured to be smaller than the dimensions of the exhaust valve 32and the suction valve 22, which is disposed adjacent to the exhaustvalve 32. Circulating exhaust gas emitted from the exhaust port 31 iscooled off by a cooling unit 112 set to an exhaust circulating port 111,which is then led to the exhaust port 41, and then led into the fuelcombustion chamber via the exhaust valve 32. The capacity of the EGRsystem provided for the present embodiment is so arranged that thecapacity becomes short when the six-cycle engine outputs a high power.Hence, the EGR system is compactly configured due to the short capacity.When the six-cycle engine outputs low power, the suction valve does notopen itself during the introduction of scavenging air stroke, but itadmits scavenging air only from the scavenging valve. When the six-cycleengine outputs high power, the suction valve opens itself during theintroduction of scavenging air stroke so as to feed fresh air into thefuel combustion chamber to compensate the shortage of the scavengingair. Concretely, the suction valve is open during the introduction ofscavenging air stroke when the above engine is driven with a more thanpredetermined number of the revolution and a more than predeterminedaperture degree of the throttle valve. The aperture degree is maximizedat a point close to the maximum power output from the six-cycle engine.FIG. 16 illustrates a map for controlling the aperture degree of thesuction valve during the introduction of scavenging air stroke.

FIG. 8 is a schematic diagram of the continuously variable valve timingdriving system for driving the suction valve according to the presentembodiment. Although being similar to the system shown in FIG. 3, thesystem shown herein is provided with a valve lifter 127 that follows upa locker arm having a greater operative angle relative to a couple oflocker arms 146 and 146B so as to solely drive the suction valve 22. Thecontrolling shaft 123 varies the aperture degree of the suction valve 22used as the first valve during the suction stroke. The controlling shaft123B varies the aperture degree of the suction valve 22 during theintroduction of air scavenging stroke. In the present embodiment, thecontrolling shafts 123 and 123B are not interlinked via the linkingmechanism, but the shaft 123B is solely operated by an actuator 91B thatis independently driven.

SEVENTH EMBODIMENT

FIG. 9 is a cross-sectional view of a cam shaft 130 built in thevariable valve timing mechanism provided for the six-cycle engineaccording to the seventh means for solving problems. All thevalve-driving cam shafts including the present cam shaft 130 make a fullturn while the crank fully rotates three times. The 12 o'clock directionindicated by the cam shown in FIG. 9 corresponds to the top dead centerpoint at which the piston starts off the explosion and expansion stroke,and the cam shaft 130 built in the six-cycle engine rotates in thecounterclockwise direction. The cam shaft 130 is provided with two kindsof cam. The cam 131 shown on the front side in FIG. 9 is used fordriving the exhaust valve 32 in the normal mode (hereinafter referred toas “normal-mode cam”). The cam 131 causes the exhaust valve 32 to beopened during the exhaust stroke and the scavenging air exhaustingstroke. The other cam shown on the back of FIG. 9 is a warming-up cam132, which causes the exhaust valve to be opened even when theintroduction of scavenging air stroke is underway.

FIG. 10 is a graphic chart illustrating the accelerating rate and thevalve lifting height of the exhaust valve relative to the rotating angleof the crank built in the six-cycle engine using the exhaust valve camshaft according to the present embodiment. The longitudinal axis of thegraph shown in the upper side shows the accelerating rate preset of theexhaust valve, where the acceleration rate in the direction of openingthe exhaust valve is shown in a positive sign. The longitudinal axis ofthe graph shown in the lower side shows the valve-lifting height of theexhaust valve. The lateral axis designates the rotating angle of thecrank. The crank makes a full turn for three times per cycle comprisingsix strokes. Of these, based on the point 0 degree that corresponds tothe upper dead center of the piston that sets off theexplosion/expanding stroke corresponding to the third stage stroke, atotal of 900° of the crank angles covering a total of five stage strokesranging from the third stage stroke of the explosion/expansion,discharge of exhaust gas, introduction of scavenging air, scavenging airexhausting, and the suction, up to the first stage stroke of thefollowing cycle is designated by way of dividing 900° into 180° as ascaling unit.

The dotted line shown in FIG. 10 shows the preset accelerating velocityand the valve lifting curve of the normal cam 131 for the exhaust valve.There are buffering portions indicated by slightly tilted straight linesat the initial and ending portions of the valve lifting curve. The valvelifting movement is initiated at preset accelerating velocity of thevalve at the ending point of the initial buffering portion. It is soarranged that the preset acceleration rate continuously lasts in a rangebelow a certain accelerating rate. Due to continuity of the acceleratingrate, as a whole, the valve lifting curve takes a mild curve. Whenanalyzing the crank angle at the one-eighth height of the maximum valvelifting range, not only in the case of the exhaust stroke, but also inthe case of the scavenging air exhausting stroke, the normal cam has acam profile configured such that valve starts opening at 30° before thebottom dead center and closes at 5° after the top dead center, whichcomprises 215° degrees in total.

The preset accelerating rate and the valve lifting curve of thewarming-up cam 132 according to the present embodiment are respectivelyset as shown via solid lines. The valve open angle of the warming-up camin the exhaust stroke is identical to that of the cam for the normalmode. Clearance between the valve and the piston near the top deadcenter is the same as that of the normal cam. However, after passing thetop dead center, unlike the normal cam, the valve does not seat onto thevalve seat, but it resumes a lifting movement. When the valve exceedsthe maximum cam lifting height set by the normal mode, the liftingheight provisionally becomes constant. When the valve approaches themaximum cam lifting point during the scavenging air discharging strokein the normal mode, the valve again accelerates own movement in theseating direction in same the manner as the normal cam until beingseated in position. The warming-up cam always has the same liftingheight as or a larger lifting height than the normal cam. Thisarrangement makes it possible to use the simplified variable valvetiming mechanism as cited in the above-referred Japanese PatentPublication 2.

In the present embodiment, the minimum point of lifting the valvebetween a couple of cam peaks corresponds to the point at 26.5° afterpassing the top dead center of the angle of the crank after initiatingthe introduction of scavenging air stroke. Nevertheless, since thepiston is apart from the valve at the bottom dead center, there is noneed to close the valve and it makes it possible to maintain the valvelifting height at the maximum. Thus, it is possible to fully secure anoptimum valve aperture degree during the introduction of scavenging airstroke, and yet, it is possible to expand the valve aperture rate duringthe introduction of scavenging air stroke. The expanded aperture degreeof the valve reduces effectively the pumping loss.

EIGHTH EMBODIMENT

FIG. 11 is an overall schematic diagram of the continuously variablevalve timing driving mechanism provided for the exhaust valve 32 builtin the six-cycle engine according to the second embodiment that hasintroduced the seventh means for solving problems, in which illustrationof the cylinder head is omitted. The above mechanism is provided with anexhaust cam 131B that opens the exhaust valve 32 during the exhauststroke and a scavenging cam 132B that opens itself during theintroduction of scavenging air stroke and the scavenging air dischargingstroke, where the exhaust cam 131B and the scavenging cam 132B aresecured to a cam shaft 130 that is rotated in the clockwise direction.The above continuously variable valve timing mechanism is providedsolely for the scavenging cam 132B. An eccentric wheel 138 functioningas the fulcrum of the locker arm 136 is integrally rotated inconjunction with a controlling shaft 133 and a spring pin 139. Anotherlocker arm 136B for the exhaust cam 131 is disposed in the innerlocation of the locker arm 136, where the fulcrum of the locker arm 136Bis directly secured by a controlling shaft 133. Even when thecontrolling shaft 133 rotates, the fulcrum thus does not shift itsposition, thereby enabling the locker arm 136B to swing itself with nodifference in the operating conditions at all. The above locker arms 136and 136B both swing the valve lifter 137 so as to open the exhaust valve32. Although not being illustrated, the locker arms 136 and 136B have aspring means for pressing a cam follower against the above cams.

FIG. 11 represents the state of warming up. In this condition,rotational angle of the controlling shaft 133 causes the aperture of theexhaust valve 32 to be maximized during the introduction of scavengingair stroke. By causing the controlling shaft 133 to be rotated in theclockwise direction, the fulcrum positions of the locker arms 136 and136B are shifted in the rotating direction of the cam 132. This in turndelays the timing relative to the rotation of the cam 132 to furthercause the timing for opening and closing the exhaust valve 32 to bedelayed. Concurrently, by causing the position of the acting point for avalve lifter to be apart from a valve lifter shaft 137SH, swingingmovement of the valve lifter decreases to cause the valve lifting heightto be decreased. By causing the controlling shaft 133 to be rotated tothe right shown in FIG. 11, the exhaust valve 32 that remained openitself during the introduction of scavenging air stroke and remainedclosed at the end of the scavenging air discharging stroke graduallyretards the opening point so as to decrease the aperture degree in theintroduction of scavenging air stroke. In the meantime, the exhaustvalve 32 opens and closes itself in the exhaust stroke.

NINTH EMBODIMENT

FIG. 12 is an overall schematic diagram of the valve controlling systemthat has adopted the sixth, eighth, and the tenth means for solvingproblems. The six-cycle engine 1 according to the ninth embodiment isprovided with the first and second valves, which individually correspondto the suction valve 22 and the scavenging valve 42 respectivelyequipped with a continuously variable valve timing mechanism shown inFIG. 3. The valve controlling system is further provided with ascavenging port valve 43B according to the ninth means for solvingproblems. The suction port is disposed on the opposite side of thescavenging port, which is not illustrated in FIG. 12. The exhaust valveis provided with the continuously variable valve timing driving systemshown in FIG. 11. An exhaust gas circulating port 111 is disposedbetween the exhaust port and the scavenging port. A cooling device 112is disposed at the port 111.

The controlling computer 610 comprises the following: the first valveaperture sensor 24 that is mounted to the control shaft of the firstvalve that is operated according to the accelerator pedal that driveroperates, a means for receiving signal from a catalyst sensor 68 thatsenses temperature of exhaust gas and actual density of oxygen, and ameans for driving an actuator 91 that controls relative aperture degreesof the first and second valves according to the actual exhaustcondition. The catalyst sensor is disposed at a position at which thesensing delay rate of the sensor is substantially equal to the delayrate in the conditional variation of catalyst against the variation ofexhaust gas. Delay in the sensing operation committed by the sensor isphysically corrected. The controlling computer 610 is further providedwith a sensor 52 that detects the actual number of the rotation of thesix-cycle engine. The controlling computer 610 is further provided witha function that drives another actuator 94 that opens and closes valve43B so as to provide the scavenging port with fresh air enough tosuffice shortage of circulating exhaust gas needed for admittingscavenging air. The above controlling computer 610 is further providedwith a function that drives another actuator 93 that causes thecontrolling shaft of the exhaust valve to be rotated.

FIG. 13 is an operational flowchart that illustrates control of drive ofthe actuator 91 according to the present embodiment. After completing awarming-up process, when the exhaust gas temperature value detectedreaches an appropriate level, the actuator 91 is set to a normalposition, where the first and second valves are respectively providedwith a proportional aperture degrees. If a high temperature has beendetected from the exhaust gas or if it is anticipated that temperatureof the exhaust catalyst will rise, the actuator will push thecontrolling rod forward to cause the aperture degree of the second valveto increase relatively. If a low temperature has been detected from theexhaust gas, or if it is anticipated that temperature of the exhaustcatalyst will lower, the actuator will pull the controlling rod so as todecrease the aperture degree of the second valve. Since the logic of thecontrol is simple, it is not always necessary to use a computing means.For example, it is also practicable to control such a system that drivesthe actuator by applying thermally expansible fluid.

FIG. 14 is a graphical map that illustrates aperture degree of thesecond valve relative to that of the first valve in proportion to thevalue of the detected temperature of exhaust gas according to thepresent embodiment Whenever executing an electronic controlling method,the present map is applicable in order that the second valve shallconstantly remain within an operable range.

FIG. 15 is a controlling map that illustrates the practical timing forcausing the exhaust valve 32 to be opened in response to the actualvalue of the detected temperature of the exhaust gas. The numericalangular values shown therein designates the crank angles to show theactual angular point at which the exhaust valve is opened from thebottom dead center of the piston that corresponds to the terminatingpoint of the introduction of scavenging air stroke. Basically, whentemperature remains below a predetermined degree, the open angle widensin the scavenging stroke. When temperature remains above a predetermineddegree, the open angle is gradually decreased. When the first valve isclosed, since it is not necessary to open the exhaust valve 32 duringthe introduction of scavenging air stroke, open angle is also decreased.Even when the open angle has the minimum value, the first valve isclosed at a point corresponding to 10° after passing the bottom dealcenter in order to secure the valve lifting height in the scavengingstroke. The controlling computer 610 computes an operational targetvalue of the actuator 93 via the present map for individually detectedvalues to drive the actuator to an optimal position. Since the presentembodiment applies the continuously variable valve timing mechanism, thevalve aperture degree is continuously varied. In such a variable valvemechanism that switches the cam as shown in FIG. 9; however, when theaperture and temperature of the first valve exceed a predetermined line,a switching operation is executed to shift the warming-up cam over tothe standard cam. In the present embodiment, oxygen density is adjustedby adjusting the fuel supplying volume. However, whenever opening theexhaust valve 32 in the course of admitting the scavenging air, theopening process is executed in consideration of the decrease of thevolume of the scavenging air to be introduced equivalent to the volumeof the incoming exhaust gas.

FIG. 16 illustrates a map for controlling the aperture degree of thescavenging port valve 43B for the detected value of the rotationalnumber of the six-cycle engine and also against the engine torqueaccording to the present embodiment. Initially, the controlling computer610 estimates a practical torque by referring to the detected values ofthe engine rotational number and the aperture degree of the first valve.Next, the computer 610 reads the target aperture degree of thescavenging port valve from the map by referring to the engine torque andthe detected value of the rotational number of the engine before drivingthe actuator 94 to a proper position. Basically, it is so arranged thatthe scavenging port valve 43B is opened in a range being short ofscavenging air for the volume of circulating gas that can be supplied soas to admit fresh air being short. For this reason, the same effect canbe achieved by detecting the decreased pressure of the scavenging port41 to control the scavenging port valve to be opened. In the event wherelowered density of oxygen of the catalyst generates reductive atmosphereor the temperature of the exhaust is excessively high, the controllingcomputer 610 executes a corrective operation in the direction toincreasing the proportion of fresh air, in other words, in the directionto opening the scavenging port valve 43B.

It is reported that the six-cycle engines have been used for fuelconsumption racing cars. The results evidenced that the six-cycleengines have high potentials in economy of fuel consumption. However,concrete details of the six-cycle engines used for the racing cars havenot been disclosed to the concerned. On the other hand, the four-cycleengines have thus far been consummated technologically in the market.Compared to the four-cycle engines, it was anticipated that thesix-cycle engines generates a less number of internal explosion in anidentical number of the rotation, leading to lowering power output.Hence, there has been no sign of positive study thus far made so as toprepare a full-scale mass production of the six-cycle engines.Nevertheless, as a result of practical study, a variety of advantagescited below have been realized, which include the following.

1: Fuel consumption efficiency is improved because compression ratio canbe increased,2: Charging efficiency is improved because temperature inside the fuelcombustion chamber of the six-cycle engine during the suction stroke islower than that of the four-cycle engines,3: Denser air-fuel mixture can be used because when the fresh-suctionstroke is set off, scavenging gas remains in the fuel combustionchamber, in other words, oxygen still remains therein.

Due to the above reasons, it has become obvious that the six-cycleengine is essentially capable of generating an output power close tothat can be generated by the four-cycle engines with the samedisplacement.

Further, the means for solving problems embodied by the presentinvention has successfully established various means for preciselycontrolling actual condition of built-in catalyst thus far beingapprehensive. In consequence, all the apprehensive problems have fullybeen solved. In summary, the six-cycle engine according to the presentinvention is applicable to all the applications requiring fuel-economyinternal combustion engines.

1-10. (canceled)
 11. A six-cycle engine having a suction port and ascavenging port, comprising a system that can substitute exhaustcirculating gas for the entire volume of scavenging gas.
 12. Thesix-cycle engine of claim 11, further comprising a first valve disposedto the suction port and an second valve disposed to the scavenging port,said valves including means for operating in connection withaccelerating operation and means for relatively varying aperture degreesof the first valve and the second valve by operation of an actuator. 13.A premix six-cycle engine having an suction port and a scavenging portcomprising a suction valve and a scavenging valve both being openedduring an suction stroke.
 14. The six-cycle engine of claim 12, beingconfigured as a direct-injection six-cycle engine having a suction valveto be open during a scavenging air introduction stroke, thedirect-injection six-cycle engine further comprising a continuousvariable valve timing system to vary the aperture degree of the suctionvalve during the scavenging air introduction stroke.
 15. A valve controlsystem for the six-cycle engine of claim 12, comprising means fordetecting temperature of an exhaust catalyst and means for driving theactuator to relatively control the aperture degrees of the first valveand the second valve in accordance with the temperature of the exhaustcatalyst.
 16. The six-cycle engine of claim 12, further comprising: anscavenging port valve in the upstream of the scavenging port in additionto the second valve; and an port disposed to the middle position betweenthe scavenging port valve and the second valve for circulating andsupplying exhaust gas from an exhaust port.
 17. A valve control systemfor the six-cycle engine of claim 16 having a computer for controllingthe scavenging port valve, said computer comprising: means for detectingthe conditions of the exhaust catalyst; means for detecting the aperturedegree of the first valve; and means for driving an actuator to vary theaperture degree of the scavenging port valve.
 18. A valve control systemfor the six-cycle engine of claim 14, comprising means for detectingtemperature of an exhaust catalyst and means for driving the actuator torelatively control the aperture degrees of the first valve and thesecond valve in accordance with the temperature of the exhaust catalyst.19. The six-cycle engine of claim 14, further comprising: an scavengingport valve in the upstream of the scavenging port in addition to thesecond valve; and an port disposed to the middle position between thescavenging port valve and the second valve for circulating and supplyingexhaust gas from an exhaust port.